[Docs] Migrate to new documentation format

[hramos]

Now that the Component and API docs are no longer auto-generated, we need to consolidate on a new format for our jsdoc comments. Any help from the community will be appreciated.

In this initial pull request, we'll be tackling the following docs:

• AccessibilityInfo, an API doc.
• ActivityIndicator, a Component doc.
• View, a Component doc.

This top comment will serve as a style guide, and when in doubt, please refer to the individual commits in this PR.

Each commit should update a single component or API, along with any relevant markdown files.

• Documentation in the JavaScript source files should be succinct. Any verbosity should be moved over to the markdown docs in the website...
• ...by adding a link to the relevant method/prop on the website to every comment block.
• Avoid markdown style links in JavaScript source files, opt for plain old URIs.

Let code document itself:

• If a method is Flow typed, the comment block does not need to repeat this information.
• If a param can be one of several values, and the type definition is easily determined from the code, the values should not be repeated in the comment block. Again, move this to the markdown doc if not present already.

[facebook-github-bot]

@hramos is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.